U.S. patent number 3,634,746 [Application Number 05/083,566] was granted by the patent office on 1972-01-11 for monitor for servosystems.
This patent grant is currently assigned to Sperry Rand Corporation. Invention is credited to Robert J. Strege, Sr..
United States Patent |
3,634,746 |
Strege, Sr. |
January 11, 1972 |
MONITOR FOR SERVOSYSTEMS
Abstract
Apparatus for monitoring the operation of servosystems. The
apparatus includes a dynamic monitor for providing a failure signal
in accordance with the comparison between the rate of change of the
servo displacement feedback signal and the servo rate feedback
signal. The apparatus also includes a polarity monitor for
providing a failure indication whenever the servo rate feedback
signal is not of the proper polarity so that the servo displacement
error signal is reduced.
Inventors: |
Strege, Sr.; Robert J.
(Phoenix, AZ) |
Assignee: |
Sperry Rand Corporation
(N/A)
|
Family
ID: |
22179173 |
Appl.
No.: |
05/083,566 |
Filed: |
October 23, 1970 |
Current U.S.
Class: |
318/565; 244/192;
244/194 |
Current CPC
Class: |
G05D
1/0077 (20130101) |
Current International
Class: |
G05D
1/00 (20060101); G05b 023/02 () |
Field of
Search: |
;318/561,565,564
;244/77 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dobeck; Benjamin
Claims
I claim:
1. A monitor for servoes responsive to command signals and having
displacement and rate feedback signals comprising
means responsive to said command signals and said displacement
feedback signal for providing an error signal in accordance with
the difference therebetween,
means responsive to said error signal and said rate feedback signal
for providing a first monitor signal in accordance with a
comparison of the polarities thereof,
means for deriving the rate of change of said displacement feedback
signal thereby providing a derived displacement feedback signal
functionally compatible with said rate feedback signal, and
comparison means responsive to said derived displacement feedback
signal and said rate feedback signal for providing a second monitor
signal in accordance with a comparison therebetween,
said first and second monitor signals being representative of
malfunctions of said servo.
2. The monitor of claim 1 in which said rate of change deriving
means comprises means having a transfer function in accordance with
(.tau. S)/(.tau. S+1).
3. The monitor of claim 2 further including means for lagging said
rate feedback signal in accordance with the transfer function
(1)/(.tau.S+1) thereby rendering said rate feedback signal
dynamically compatible with said derived displacement feedback
signal.
4. The monitor of claim 1 in which said comparison means
includes
means for providing a signal representative of the difference
between said derived displacement signal and said rate feedback
signal, and
dead zone means responsive to said difference signal for providing
said second monitor signal in accordance with the magnitude of said
difference signal exceeding a predetermined threshold.
5. The monitor of claim 1 further including output means responsive
to said first and second monitor signals for providing a monitor
output signal in accordance with said first and second monitor
signals representing malfunctions of said servo.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to servosystem monitors particularly of the
type suitable for use with aircraft servosystems.
2. Description of the Prior Art
Aircraft servo monitors are known that utilize analog models that
simulate the operation of the servo being monitored and provide
signals in response to the servo input signals for comparison with
the actual servo responses. Such monitors have the disadvantage
that for moderately sophisticated servosystems, the servo model
becomes unduly complex. In addition, the servo models are often not
accurately representative of the servo monitored particularly for
complex systems. Servo characteristics such as nonlinearities and
saturation, as well as second order effects, are often not
representable by analog models of reasonable complexity.
Prior art servo monitors of the analog model type have been found
subject to nuisance tripping due to transient input signals of the
type commonly encountered in normal aircraft operation.
The analog models utilized for monitoring dual channel servosystems
having differential coupling driving the output member, a servo
type used in modern jet transports, are unduly complicated
particularly with regard to the model of the differential
coupling.
SUMMARY OF THE INVENTION
The above prior art disadvantages are obviated by apparatus in
accordance with the present invention wherein a polarity monitor
provides a first monitor signal in accordance with a comparison of
the polarities of the servo displacement error signal and the servo
rate feedback signal.
A dynamic monitor is included for comparing the magnitudes of the
servo rate feedback signal and the rate of change of the servo
displacement feedback signal thereby providing a second monitor
signal.
The first and second monitor signals represent the occurrence of
malfunctions of the servo and provide a monitor output signals in
accordance therewith.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block schematic diagram of a monitor in accordance with
the principles of the present invention.
FIG. 2 is a waveform diagram useful in understanding the operation
of the monitor of the present invention when monitoring a normally
functioning servo; and
FIG. 3 is a waveform diagram useful in understanding the operation
of the monitor of the present invention when monitoring a
malfunctioning servo.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The principles of the present invention as hereinafter described
are applicable to the monitoring of a wide variety of servosystems.
The monitor will be described, for purposes of explanation, in
terms of a dual-channel servosystem for positioning the elevator
control surface of an aircraft. Such a servosystem is illustrated
in FIG. 2 of U.S. Pat. No. 3,504,248 entitled, Dual Channel Servo
System Having Torque Equalization, by H. Miller, Issued Mar. 31,
1970, and assigned to the assignee of the present invention. The
monitor will be explained in terms of servo channel 2 of FIG. 2 of
the dual servosystem illustrated in said U.S. Pat. No.
3,504,248.
Referring to FIG. 1, a monitor 10 is illustrated comprising a
polarity monitor 11 and a dynamic monitor 12. The polarity monitor
11 comprises a summing circuit 13 to which are applied as inputs an
equalization signal, a servo command signal and a displacement
feedback signals on leads 14, 15 and 16 respectively. The signals
on the leads 14, 15 and 16 may be derived, with respect to FIG. 2
of said U.S. Pat. No. 3,504,248, from the integrator 55, the servo
command input A, and the synchros 19 and 51, respectively. The
summing circuit 13 subtracts the servo displacement feedback signal
on the lead 16 from the sum of the command signal on the lead 15
and the equalization signal on the lead 14 to provide an error
signal representative of the servo displacement error signal on a
lead 17. The signal on the lead 17 is representative of the actual
servo displacement error signal provided by servoamplifier 5 of
FIG. 2 of said U.S. Pat. No. 3,504,248.
The signal on the lead 17 is applied as an input to an error
polarity sensor and dead zone circuit 20. The circuit 20 provides a
signal on a lead 21 whenever the error signal on the lead 17
exceeds a predetermined threshold. When the error signal exceeds
the threshold and is of a positive polarity, the signal on the lead
21 is representative of the positive polarity. Similarly, when the
error signal exceeds the threshold and is of a negative polarity,
the signal on the lead 21 is representative of the negative
polarity. The dead zone portion of the circuit 20 is included to
compensate for differences in nulls of the system.
The polarity monitor 11 additionally includes a tachometer polarity
sensor and dead zone circuit 22. The circuit 22 received as an
input signal on a lead 23, the rate feed back signal from the
tachometer generator 12 of FIG. 2 of said U.S. Pat. No. 3,504,248.
The circuit 22 provides a signal on a lead 24 whenever the rate
feedback signal on the lead 23 exceeds a predetermined threshold.
The signal on the lead 24 is representative of the polarity of the
rate feedback signal on the lead 23 in a manner similar to that
described with respect to the circuit 20.
The signals on the leads 21 and 24 are applied as inputs to a logic
circuit 25. The logic circuit 25 provides a first monitor signal on
a lead 26 representative of servo malfunction. Ordinarily, the
signal on the lead 26 is low representing a normally functioning
servo. When a servo error signal exists on the lead 17 exceeding
the dead zone of the circuit 20, the signal on the lead 26 becomes
high if a tachometer signal does not exist on the lead 23 exceeding
the dead zone of the circuit 22 and of a polarity so that the servo
operates to reduce the error signal. A high signal on the lead 26
is representative of a malfunctioning servo. For example, when a
positive servo error signal on the lead 17 exceeds the dead zone of
the circuit 20, the tachometer signal on the lead 23 must exceed
the dead zone of the circuit 22 and be of a negative polarity to
maintain the signal on the lead 26 low. Similarly, when a negative
servo error exceeds the dead zone of the circuit 20, the tachometer
signal must exceed the dead zone of the circuit 22 and be of a
positive polarity to maintain the signal on the lead 26 low.
It will be appreciated that the polarity monitor 11 permits any
magnitude of servo displacement error to exist without indicating
malfunction if the servo motor is turning in the proper direction
to reduce the error.
From the foregoing it will be appreciated that the polarity monitor
11 detects failures in the servoamplifier and the servomotor as
well as in the tachometers of the servo loop. Failures such as open
windings and open circuits or frozen bearings are detectable by
means of the polarity monitor 11.
Although the monitor 10 has been described in terms of a servo
system having equalization, it is appreciated that the principles
of the invention are equally applicable to servoes without
equalization. When utilizing the invention in such a servo, the
equalization input lead 14 would not be utilized. Similarly, if the
equalization signal is summed with the command signal upstream of
the servoamplifier input, only this summed signal would then be
applied to the monitor. For purposes of operation of the monitor
10, the equalization signal may be considered as part of the total
command input to the servo.
The dynamic monitor 12 of the monitoring apparatus 10 includes a
summing circuit 30. The circuit 30 provides a signal on a lead 31
representative of the rate feedback signal of the Servosystem being
monitored. The signal on the lead 31 is comprised of the sum of the
tachometer signal on the lead 23 and the tachometer signal on the
lead 32. As previously mentioned, the tachometer signal on the lead
23 is derived from the tachometer generator 12 of FIG. 2 of said
U.S. Pat. No. 3,504,248. Similarly, the signal on the lead 32 is
derived from the tachometer generator 20 of said patent.
The servo rate feedback signal on the lead 31 is applied as an
input to a lag network 33. The lag network 33 has a transfer
function of (1)/(.tau.S1) and provides the lagged rate feedback
signal on a lead 34 for reasons to be explained.
The dynamic monitor 12 further includes a rate network 35 deriving
its input from the servo displacement feedback signal on the lead
16. The rate network 35 differentiates the displacement feedback
signal on the lead 16 in accordance with the transfer function
(.tau. S)/(.tau.S 1) providing a signal on a lead 36 representative
of the rate of change of the displacement feedback signal.
It will now be appreciated that the servo rate feedback signal on
the lead 31 is lagged by the lag network 33 with a time-constant
equal to that of the rate network 35 so as to produce a dynamic
match between the signals on the leads 34 and 36 in accordance with
the equation
The dynamic match will be proper when .tau..sub.1 =.tau..sub.2 and
K.sub.P .tau..sub.1 =K.sub.T.
The signals on the leads 34 and 36 are applied as inputs to a
summing circuit 37. The circuit 37 subtracts the signal on the lead
34 from the signal on the lead 36 providing the difference
therebetween on a lead 40.
The difference signal on the lead 40 is applied as an input to an
absolute value sensor and dead zone circuit 41. The circuit 41
provides a high signal on a lead 42 whenever the absolute value of
the signal on the lead 40 exceeds a predetermined threshold, a low
signal otherwise being provided thereon. The dead zone of the
circuit 41 is included to eliminate nuisance triggering of the
dynamic monitor 12. The signal on the lead 42 provides a second
monitor signal to a lead 43 via an inverter 44, the second monitor
signal being representative of the operation of the servo being
monitored. A low signal on the lead 43 is representative of a
malfunctioning servo.
It will now be appreciated that the dynamic monitor 12 detects
failures in the displacement feedback loop of the servosystem being
monitored. In the dual channel servo of said U.S. Pat. No.
3,504,248 the displacement feedback signal represents the elevator
jackscrew position and is actually the sum of both servo motor
positions of the two channels as explained in said Patent. The rate
of change of this displacement feedback signal is derived in the
rate network 35 and then compared to the actual actuator rate in
the circuits 37 and 41. The actual actuator rate is obtained in the
dual servo system of said Patent by summing the tachometer signals
of both channels in the summing circuit 30. If the comparison
between the derived servo rate and the actual servo rate produces
an error signal on the lead 40 that is in excess of the dead zone
of the circuit 41, regardless of the polarity of the error, the
second monitor signal on the lead 43 will become low indicating a
malfunction in the servo displacement feedback path.
The first monitor signal on the lead 26 is applied to an inverting
input of an output AND-gate 45. The second monitor signal on the
lead 43 is applied as another input to the AND-gate 45. The
AND-gate 45 provides a monitor output signal on a lead 46 which may
be applied to the brake 36 of FIG. 2 of said U.S. Pat. No.
3,504,248 for the reasons explained therein. It will be appreciated
that the signal on the lead 46 will be high in the absence of servo
malfunctions. Should the signal on the lead 26 become high or the
signal on the lead 43 become low because of a servo malfunction,
the signal on the lead 46 will become low thereby applying the
brake 36 in the manner described in said U.S. Pat. No.
3,504,248.
It will be appreciated that a delay device may be utilized to
couple the signal on the lead 46 to the brake 36 to prevent
nuisance triggering of the monitor due to transient conditions
normally encountered in aircraft operation. Such transients may
occur because of gust and turbulence loading of the aircraft.
Should a servo malfunction occur, it is often desirable to latch an
indicator on so that the indicator remains on until the monitor is
reset by the pilot. To accomplish this, conventional circuits, not
shown, responsive to the signal on the lead 46 may be utilized to
apply an error condition to the monitor input so as to maintain the
failure indication until the circuits are reset.
Referring to FIG. 2, waveforms are illustrated representing the
operation of the monitor 10 when the servosystem being monitored is
functioning properly. Curve 100 represents a variety of command
input signals that may be encountered in aircraft flight modes. It
is observed from curve 101 that a normally operating servosystem
does not trigger the dynamic monitor 12. FIG. 3, however,
illustrates tripping of the dynamic monitor 12 due to both an open
displacement feedback failure and a hard-over displacement feedback
failure. It should be noted from curves 102 and 103 of FIGS. 3 and
4 that the polarities of the rate feedback signal and the servo
displacement error signal are such as not to trigger the polarity
monitor 11.
It will be appreciated that although the preferred embodiment of
the invention was described in terms of a dual channel servosystem,
the principles of the invention are equally applicable to single
channel servosystems.
It is further appreciated that from the waveforms 100 of FIG. 2
that the monitor of the present invention is insensitive to the
type of the command input signal and will provide failure
indications only for servo malfunctions.
While the invention has been described in its preferred embodiment,
it is to be understood that the words which have been used are
words of description rather than limitation and that changes may be
made within the purview of the appended claims without departing
from the true scope and spirit of the invention in its broader
aspects.
* * * * *